Communications systems

a technology of communication systems and communication channels, applied in the field of communication systems, can solve the problem of relatively small overhead, and achieve the effect of improving the downlink capacity

Inactive Publication Date: 2006-06-15
KYOCERA CORP
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  • Abstract
  • Description
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  • Application Information

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Benefits of technology

[0015] Embodiments of the present invention can provide techniques for subcarrier allocation for a coded OFDMA system with fixed number of assigned subcarriers per subchannel. Embodiments employ channel coding, and so a metric is used which takes advantage of the channel coding properties. A low complexity algorithm is proposed that allocates the best possible subcarriers to every user based on that metric. In embodiments of the present invention, in addition to substantially improving downlink capacity, a fair subchannel distribution is employed that assigns a fixed number of subcarriers to each user and also ensures similar PER (packet error rate) and BER (bit error rate) performance for all users at the same SNR.

Problems solved by technology

However this overhead can be relatively small, especially if the channels vary slowly.

Method used

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Embodiment Construction

[0034] In an OFDM or OFDMA system, in the presence of multipath diversity, all subcarriers will arrive at a given receiver with different amplitudes. In fact, some subcarriers may be completely lost because of significant fading effects. Hence, the overall bit rate and capacity will be dominated by the few subcarriers with the smallest amplitudes (even though most subcarriers may be detected without errors).

[0035] In order to attempt to counteract this disadvantage, most OFDM or OFDMA systems employ channel coding. Using coding across the subcarriers, enables errors of weak subcarriers to be corrected. The performance of the coded OFDM / OFDMA system can be determined by the average received power rather than the power of the weakest subcarrier.

[0036] In the described embodiment of the present invention, the average received power (or channel gain) of each subchannel (user) will be used as the quality metric to allocate the subcarriers. The subcarriers are allocated in such a way as...

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Abstract

In a multi user communication system, subcarriers are allocated to subchannels using a quality measurement for each subchannel. An initial sub carrier is allocated to each subchannel, and a quality metric measured. Subsequent subcarriers are allocated in dependence upon the quality measurement for each subchannel. The subchannel with the lowest quality measurement receives the first allocation, and the subchannel with the highest quality measurement receives the last allocation. The subsequent allocation is repeated, following a re-sort of the subchannel quality measurements, until all of the subcarriers are allocated.

Description

[0001] The present invention relates to communications systems, and to dynamic multi-user subcarrier allocation in a coded OFDMA (orthogonal frequency division multiple access) radio frequency communications system in particular. BACKGROUND OF THE PRESENT INVENTION [0002] In a frequency selective fading channel, different subcarriers will experience different channel gains. In traditional OFDM (Orthogonal Frequency Division Multiplex) TDMA (time division multiple access) systems each user transmits on all sub-carriers simultaneously and users share the channel in time. If the channel is perfectly known to the transmitter, the so-called “water-filling” policy (that is, more power when the channel gain is high and less power when the channel gain is low) is known to be optimal in maximising the data rate. The increase of data rate, by using transmit power allocation in a single user OFDM system is due to spectral diversity effects. [0003] In OFDMA systems, users do not share the chann...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): H04K1/10H04L5/02H04W72/08
CPCH04L5/0007H04L5/006H04W72/08H04W72/54H04B1/69H04B13/00H04J11/00H04L27/26
Inventor ARMOUR, SIMONDOUFEXI, ANGELAGEERTVAW, JOSEPH MC
Owner KYOCERA CORP
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